Rubber composition and rubber products using same

ABSTRACT

Compositions useful for power transmission belts or hose which utilize environmentally friendly cellulosic reinforcing fibers. The elastomeric or rubber compositions include a base elastomer, polyvinylpyrrolidone, a cellulosic fiber, and a curative. The base elastomer may be one or more selected from ethylene elastomers, nitrile elastomers, and polychloroprene elastomers. The elastomer may be an ethylene-alpha-olefin elastomer. The polyvinylpyrrolidone may be present in an amount of 5 to 50 parts weight per hundred parts of the elastomer. The cellulosic fiber may be one or more selected from kenaf, jute, hemp, flax, ramie, sisal, wood, rayon, acetate, triacetate, and cotton. The cellulosic fiber may be a bast fiber. The cellulosic fiber is present in an amount of 1 to 50 parts weight per hundred parts of the elastomer.

This application is related to U.S. patent application Ser. No.13/692,585 filed Dec. 3, 2012, and to U.S. provisional application No.61/569,744 filed Dec. 12, 2011, the entire contents of both of which arehereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to a rubber composition useful forrubber products such as belts and hose, more particularly to acomposition that is a blend of polyvinylpyrrolidone in an elastomer,reinforced with cellulosic fibers.

Belts for power transmission include V-belts, multi-v-ribbed belts, andsynchronous or toothed belts. High-performance, synthetic, short-fiberreinforcements, such as aramid fibers, are often used in the rubberformulations used in such belts. These fibers tend to be expensive andfrom non-renewable sources, but are considered necessary to meetperformance requirements.

SUMMARY

The present invention is directed to systems and methods which provideelastomeric compositions useful for power transmission belts or hosewhich utilize environmentally friendly cellulosic reinforcing fibers.

The elastomeric or rubber compositions include an elastomer,polyvinylpyrrolidone, a cellulosic fiber, and a curative.

The elastomer may be one or more selected from ethylene elastomers,nitrile elastomers, and polychloroprene elastomers. The elastomer may bean ethylene-alpha-olefin elastomer.

The polyvinylpyrrolidone may be present in an amount of 5 to 50 partsweight per hundred parts (“PHR”) of the elastomer.

The cellulosic fiber may be one or more selected from kenaf, jute, hemp,flax, ramie, sisal, wood, rayon, acetate, triacetate, and cotton. Thecellulosic fiber may be a natural fiber or man-made material. Thecellulosic fiber may be a bast fiber. The cellulosic fiber is present inan amount of 1 to 50 parts weight per hundred parts of the elastomer.

The invention is also directed to a power transmission belt utilizingthe reaction product of the inventive rubber composition. The rubbercomposition may be vulcanized or cured.

The invention may contribute to providing relatively high value rubbercompounds, for example, achieving a relatively high compound moduluswith a relatively low-cost fiber from a renewable natural resource.

Embodiments of the invention based on polychloroprene elastomer mayexhibit a modulus plateau on cure instead of a marching modulus.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe scope of the invention as set forth in the appended claims. Thenovel features which are believed to be characteristic of the invention,both as to its organization and method of operation, together withfurther objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification in which like numerals designate like parts,illustrate embodiments of the present invention and together with thedescription, serve to explain the principles of the invention. In thedrawings:

FIG. 1 is a partially fragmented perspective view of a powertransmission V-belt according to an embodiment of the invention;

FIG. 2 is a cross-section view of a power transmission V-ribbed beltaccording to an embodiment of the invention; and

FIG. 3 is a partially fragmented perspective view of a toothed powertransmission belt according to an embodiment of the invention.

DETAILED DESCRIPTION

The invention is directed to rubber compositions useful for dynamicproducts such as power transmission belts or hose. The rubbercompositions have a base elastomer blended with polyvinylpyrrolidone(PVP) and have a cellulosic fiber component.

The term “rubber” refers to a material capable of recovering from largedeformations quickly and forcibly (i.e., is “elastomeric”), and which isessentially insoluble in boiling solvents (due the presence of covalentcrosslinks). Other useful definitions may be found in ASTM D-1566, whichis hereby incorporated herein by reference. “Elastomer” refers to anelastomeric polymer, which when crosslinked may form a rubber.

Rubber or elastomeric “composition” or “formulation” refers to thecombination of raw materials used to make a rubber material. Rubber“compound” refers to the mixture of the materials in a rubbercomposition after mixing but before curing or vulcanization. Rubbercompositions may include a number of additional ingredients besides theelastomer(s), such as curatives, fillers, extenders, softeners,anti-degradants, colorants, process aids, curatives, accelerators,retardants, coagents, flame retardants, and the like. “Base elastomer”refers to the elastomeric polymer used in the rubber composition, and itmay be a blend of elastomers.

The inventive rubber may be based on any suitable base elastomer, butexemplary elastomers are natural rubber, polychloroprene (CR),polyisoprene, styrene-butadiene rubber, ethylene elastomers, nitrileelastomers, polyurethane elastomers, and the like. Ethylene elastomersinclude ethylene-vinylacetate elastomer, ethylene acrylic elastomers,and ethylene-alpha-olefin elastomers. Nitrile elastomers includeacrylonitrile-butadiene rubber (NBR), hydrogenated nitrile (HNBR),carboxylated NBR and HNBR, and the like. The invention is particularlyadvantageous when the exemplary rubber compositions are based onnon-polar elastomers such as the ethylene-alpha-olefin elastomers, suchas ethylene propylene diene elastomer (EPDM), ethylene propyleneelastomer (EPM), ethylene octene elastomers (EOM), ethylene buteneelastomer (EBM), and the like. The rubber compositions may also be basedon blends of two or more elastomers.

The inventive rubber is based on a blend of a base elastomer andpolyvinylpyrrolidone as the polymeric matrix in which all otheringredients are mixed. Polyvinylpyrrolidone (PVP) is a white,hygroscopic powder with a weak characteristic odor. In contrast to mostpolymers, it is readily soluble in water and a large number of organicsolvents, such as alcohols, amines, acids, chlorinated hydrocarbons,amides and lactams. On the other hand, the polymer is insoluble in thecommon esters, ethers, hydrocarbons and ketones. The hygroscopicproperty combined with outstanding film formation, initial tack andadhesion to different materials, high capacity for complex formation,good stabilizing and solubilizing capacity, insensitivity to pH changes,ready radiation-induced crosslinkability as well as good biologicalcompatibility have made PVP a frequently used specialty polymerespecially in solutions, emulsions, coatings, and films.

PVP is synthesized by free-radical polymerization of N-vinylpyrrolidonein water or alcohols with a suitable initiator and method oftermination. By selecting suitable polymerization conditions, a widerange of molecular weights can be obtained, extending from low values ofa few thousand daltons to approximately 2.2 million daltons. Selectedcomonomers can be incorporated into the PVP polymer duringpolymerization to modify its properties. Such comonomers includevinylacetate (VA) and N-vinylcaprolactam (VCAP). For example, Luvitec®VA64 contains about 40% of VA comonomer and is less hygroscopic than PVPhomopolymer. Table 1 shows weight average and number average molecularweight in Daltons of some commercial PVP homo- and co-polymer gradesfrom BASF sold under the Kollidon® mark and the Luvitec® mark.

TABLE 1 Number Grade Weight Average Average Kollidon ® 12PF 2000-30001300 Kollidon ® 17PF  7000-11000 2500 Kollidon ® 25 28,000-34,000 6000Kollidon ® 30 44,000-54,000 12,000 Kollidon ® 90F 1,000,000-1,500,000360,000 Luvitec ® K17   9000 2000 Luvitec ® K30 50,000 14,000 Luvitec ®VA64 65,000 15,000

The present invention is directed to the use of cellulosic fibers, whichare naturally occurring plant-derived fibers or man-made fibers with amajor component based on cellulose, such as wood, kenaf, jute, hemp,ramie, and flax, in rubber compositions useful for flexible powertransmission belts or hose. The bast fibers from the bark section of theplants are of primary interest, although some leaf and seed fibers mayalso be useful. Other bast fibers include sunn, urena or cadillo, androselle. Leaf fibers include abaca, cantala, henequen, istle, phromium,sanseviera, and sisal. Useful seed fibers include cotton and kapok. Woodfibers include those derived from hardwood or softwood species. Man-madecellulosic fibers include rayon (regenerated cellulose), viscose,acetate (cellulose acetate), triacetate (cellulose triacetate), and thelike.

Kenaf (Hibiscus cannabinus L.) is an annual herbaceous plant originallyfrom Africa. It is a newer crop to the United State. Kenaf is mainlycultivated in southern temperate regions such as Mississippi, Texas,California, Louisiana, New Mexico, and Georgia. It has a growing periodof 90-150 days and may grow to 2.4-6 m in height. Its single, straightstem consists of an outer fibrous bark and an inner woody core whichyields two distinct types of fibers: bast and core fibers respectively.The bast fiber constitutes about 26-35 wt % (weight percentage) of itsstem, and genetic strains have been developed which yield 35 wt % orgreater bast portions. The harvested kenaf stems are usually firstdecorticated to separate the bark from the core, producing ribbons ofkenaf bast fibers. These ribbons can be retted into fiber bundles orsingle fibers. It is preferable to harvest the kenaf crop once the fiberhas been air-dried (approximately 10% moisture content). Drying may beachieved by leaving the crop standing in the field.

In general, the kenaf bast fibers are hollow tubes averaging 2.6 mm inlength, 21 μm in diameter with an average length/diameter aspect ratioof 124, very similar to softwood species. The core fibers, with anaverage length of 0.5 mm, closely match those of hardwoods.

The major constituents of kenaf bast fiber bundles (KBFB) are cellulose,hemicellulose and lignin. The amount of each constituent can varysignificantly due to cultivation environments, geographic origins, age,locations in the plant (from root to tip), and retting and separatingtechniques. Lloyd E. H. and D. Seber, “Bast fiber applications forcomposites,” (1996), available at http://www.hempology.org/CURRENT%20HISTORY/1996%20HEMP%20COMPOSITES. html, reported weight percentagesof 60.8 for cellulose, 20.3 for hemicellulose, 11.0 for lignin, 3.2 forextractives, and 4.7 for ash. Mohanty et al, “Biofibres, biodegradablepolymers and biocomposites: an overview,” Macromolecular materials andengineering, 276-277(1):1-24 (2000), reported lower cellulose (31-39 wt%) and higher lignin (15-19 wt %) amounts. Rowell et al.,“Characterization and factors effecting fiber properties,” In: FrolliniE, Leão A L, Mattoso LHC, editors. “Natural polymers and agrofibersbased composites: preparation, properties and applications,” San Carlos,Brazil: L.H.C., Embrapa. pp. 115-134 (2000) reported 44-57 wt %cellulose, and 15-19 wt % lignin. Other sources cite cellulose contentsof about 71 to 76% for kenaf, jute, hemp and flax fibers, with lower(≤8%) lignin contents and 13-19% hemicellulose.

Kenaf is a cellulosic source with ecological and economical advantages,abundant, exhibiting low density, nonabrasive during processing, highspecific mechanical properties, biodegradable and cheap pricing.Historically, kenaf fiber was first used as cordage. Industry is nowexploring the use of kenaf in papermaking and nonwoven textiles.Potential applications of kenaf products include paper pulp, cordage,grass erosion mats, animal bedding, oil sorbents, potting media, animallitter, insulation boards, fillers for plastics, and textiles.

Table 2 compares mechanical properties of kenaf and other cellulosicfibers with some common synthetic fibers. Kenaf, flax, hemp, and juteare bast fibers, while sisal is a leaf fiber and cotton is a seed hairfiber. In terms of tensile strength and elongation, the cellulosicfibers compare quite favorably with nylon and polyester. The outstandingfeature of kenaf fiber is its Young's modulus, which is close to that ofE-glass fiber and aramid fiber. These cellulosic fibers' tensilestrength is not high enough for belt tensile cord applications, butaccording to an embodiment of the invention, they are suitable for usingas a filler to reinforce rubber belt compounds to provide belt shapestabilization or stiffening or cord support.

TABLE 2 Tensile Young's Elongation Density Diameter strength Modulus atbreak Fiber (g/cc) (μm) (MPa) (GPa) (%) Kenaf (bast) 1.45 14-23 930 531.6 Flax (bast) 1.5  40-600  345-1500 27.6 2.7-3.2 Hemp (bast) 1.4813-30 810 1-6 Jute (bast) 1.50 15-25 350-700 1.5 Sisal (leaf) 1.5511-635 9.4-22  2-3 Cotton (seed 1.5-1.6 12-38 287-800  5.5-12.6 7-8hair) Nylon 1.0-1.2 40-90 3-5 20-60 (synthetic) Polyester 1.2-1.5 40-90  2-4.5 12-47 E-glass 2.55 <17 3400 73 2.5 Kevlar 1.44 3000 60 2.5-3.7Carbon 1.78 5-7 3400-4800 240-425 1.4-1.8

Preferred bast fibers, including kenaf fibers, for practicing thepresent invention are the longer bast fibers from bark, separated fromthe shorter core fibers, and chopped to a useful length for use in beltcompositions. Suitable fiber lengths may be in the range from 0.5 to 5mm, or from 1 to 4 mm, or 1 to 3 mm or 2 to 3 mm. Preferred loadingswill depend on the amount of reinforcement desired, but mayadvantageously be in the range of 0.5 to 50 parts weight per hundredparts of the base elastomer (PHR), or from 1 to 30 PHR. Suitable fibersmay be obtained, for example, from Procotex Corporation SA, KenactivInnovations, Inc., or International Fiber Corporation.

Flax fiber (Linum usitatissimum L.) comes from the annual plant by thatname grown in temperate, moist climates. Harvesting and processing ofthe flax bast fibers is similar to Kenaf. Boiled and bleached flax maycontain over 95% cellulose. Suitable fibers may be obtained for examplefrom Procotex Corporation SA.

Hemp fiber comes from the plant Cannabis sativa which originated inChina, but is now grown in Asia and Europe as well.

Jute comes from two plants, Corchorus capsularis and C. olitorius. It isgrown mainly in India, Bangladesh, Burma, Nepal, and Brazil. Kenaf andjute contain lignocellulose, which contributes to their stiffness.Roselle is derived from H. Sabdarifa, which is closely related to kenaf.

Ramie bast fiber comes from the bark of Boehmeira nivea. Because of thehigh gum content, it cannot be retted like kenaf. Instead, the fibersare separated by boiling in alkaline solution, followed by washing,bleaching, neutralizing, and drying. Thus degummed ramie may containover 95% cellulose. Such chemical treatments may also be used to prepareother types of fibers, and may include enzyme treatments.

Sisal is obtained from Agave sisalana and is the most commerciallyimportant of the leaf fibers.

A number of other plant fibers have been studied for possible use incomposites. To the extent they are cellulosic and have suitable physicaland dimensional properties, they may also be useful in rubbercompositions. Among these others are banana plant fibers, pineapple,palm, bamboo, and the like.

Wood fiber (also known as cellulose fiber or wood pulp or just “pulp”)can be obtained from any number of wood species, both hardwood andsoftwood. The fibers may be separated by any of the known pulpingprocesses to obtain suitable fibers for reinforcing rubber compositions.Recycled pulp may be used.

The cellulosic fibers may be used in the elastomer-PVP blend compositionas the only fiber reinforcement, or other types of fibers may beincluded in addition. For example, some additional fibers such asaramid, polyamide, polyester, carbon glass or the like may be blendedwith the cellulosic fibers in the composition.

Mixing may be carried out using any conventional or known mixingequipment including internal batch mixers, open roll mills, compoundingextruders, or the like. Likewise the compositions may be shaped, formed,cured or vulcanized using any conventional or known method or equipment.

The inventive rubber compounds may be used in power transmission beltssuch as V-belts, toothed or synchronous belts, and multi-v-ribbed belts,as well as in hose or other suitable rubber products.

FIG. 1 shows a power transmission belt embodiment of the invention inthe form of a V-belt proportioned for a variable-speed drive. V-belt 100has a generally isosceles trapezoidal cross section, with tension orovercord layer 130 on the back-, upper-, outer- or top-side, andcompression or undercord layer 110 on the bottom-, lower-, orinner-side, with adhesive layer 120 in between and helically woundtensile cord 140 embedded therein. The lateral sides are the pulleycontact surfaces which define the V-shape. The layers of the belt body,including adhesion layer 120, overcord layer 130, and undercord layer110, are generally vulcanized rubber compositions, and they may bedifferent formulations from each other or the same formulation. TheV-belt may include cogs or notches on the back side, inside or both.Fabric may also be used on a surface or within the belt. The cord may beany known high modulus, fatigue resistant, twisted or cabled bundle ofpolyamide, polyester, aramid, carbon, polybenzobisoxazole, boron, orglass, fibers or yarns, or hybrids thereof, and may be treated with anadhesive, or the like. An embodiment of the inventive rubber compositioncontaining an elastomer, PVP, and cellulosic fibers may be utilized inany one or more of the elastomer layers used within a given beltconstruction. One or more layers may include dispersed short fibersoriented in the transverse direction to increase transverse stiffness ofthe belt body while maintaining longitudinal flexibility.

FIG. 2 shows a cross-section of a power transmission belt embodiment ofthe invention in the form of a V-ribbed belt. V-ribbed belt 200 hastension or overcord layer 230 on the back-side, and compression orundercord layer 210 on the bottom-side, with adhesive layer 220 inbetween and helically wound tensile cord 240 embedded therein. TheV-shaped ribs are the pulley contact surfaces. The layers of the beltbody, including adhesion layer 220, overcord layer 230, and undercordlayer 210, are generally vulcanized rubber compositions, and they may bedifferent formulations from each other or the same formulation. Fabricmay also be used on a surface or within the belt. The cord may be asdescribed for the V-belt above. An embodiment of the inventive rubbercomposition containing an elastomer, PVP, and cellulosic fibers may beutilized in any one or more of the elastomer layers used within a givenbelt construction. One or more layers may include dispersed short fibersoriented in the transverse direction to increase transverse stiffness ofthe belt body while maintaining longitudinal flexibility.

FIG. 3 shows a power transmission belt embodiment of the invention inthe form of a synchronous or toothed belt. Toothed belt 300 has tensionor overcord layer 330 on the back-side, and tooth-rubber 310 in theteeth, with tooth fabric 320 covering the teeth and helically woundtensile cord 340 embedded in the belt. The teeth are the pulley contactsurfaces. The rubber layers of the belt body, including tooth rubber 310and overcord layer 330, are generally vulcanized rubber compositions,and they may be different formulations from each other or the sameformulation. The cord may be as described for the V-belt above. Anembodiment of the inventive rubber composition containing an elastomer,PVP, and cellulosic fibers may be utilized in any one or more of theelastomer layers used within a given belt construction. One or morelayers may include dispersed short fibers which may also be oriented inan advantageous way.

Likewise, a hose embodiment (not shown) may include one or more rubberlayers, any of which may be based on the inventive rubber composition. Ahose may also include textile reinforcement layer(s) or adhesivelayer(s).

Examples

In a first series of rubber compound examples, the effect of adding PVPto an EPDM composition with kenaf or flax cellulosic fibers was studied.The compositions listed in Table 3 were mixed in conventional rubbercompounding equipment, i.e., an internal mixer followed by milling andcalendering. Comparative examples are indicated with “Comp. Ex.” andinventive examples as “Ex.”

Compound physical properties were tested using standard rubber testingmethods. Tensile strength, ultimate elongation and modulus weredetermined in the with—grain (“WG”) and cross-grain (“XG”) directionusing common tensile test methods, in accordance with ASTM D-412 (die C,and using 6″/min. crosshead speed). “Modulus” herein refers to tensilestress at given elongation (eg., 5% or 10%) as defined in ASTM D-1566and ASTM D-412. Rubber hardness was tested with a type-A durometeraccording to ASTM D-2240. Tear strength was tested according to ASTMD-624, die-C, in with—grain and cross-grain directions. Compound elasticmodulus (G′) was evaluated according to ASTM D-6204 on the RPA2000tester at 6.98% strain, 1.667 Hz, after curing the composition in thetester.

The measurement results are shown in Table 4. It was found that theaddition of PVP into the EPDM compounds having cellulosic fibersincreased the compound elastic modulus (G′), tensile strength, tensilemodulus and tear strength. For example, a comparison of Comp. Ex. 2 withEx. 3 and Ex. 4, or alternately with Ex. 5 and Ex. 6, shows increasingphysical properties with increasing levels of PVP for Kenaf-filledrubber. Likewise, a comparison of Comp. Ex. 2 with Ex. 3 and Ex. 4, oralternately with Ex. 5 and Ex. 6, shows increasing physical propertieswith increasing levels of PVP for Kenaf-filled rubber. Without intendingto be limited, these results are believed to indicate that thecompatibility between the cellulosic fiber and the non-polar EPDM rubbermatrix was improved by the addition of the polar PVP. The results alsoshow that cellulosic fibers, with the PVP-modified EPDM elastomer, canbe a viable replacement for at least a portion of the state-of-the-arthigh-performance chopped aramid fibers in Comp. Ex. 1. Thus, Ex. 3-8have comparable or better physical properties than Comp. Ex. 1.

TABLE 3 Parts by Comp. Comp. weight Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6Ex. 7 Ex. 8 EPDM 100 100 100 100 100 100 100 100 PVP¹ — — 4. 8. — — 8. —PVP² — — — — 4. 8. — 8. Fillers 88.1 88.1 88.1 88.1 88.1 88.1 88.1 88.1Paraffin 9.4 9.4 9.4 9.4 9.4 9.4 9.4 9.4 Oil Other 18.6 18.6 18.6 18.618.6 18.6 18.6 18.6 1-mm 18 10 10 10 10 10 10 10 aramid fiber 2-mm — 1515 15 15 15 — — Kenaf fiber 2-mm — — — — — — 15 15 Flax fiber Cure 6.36.3 6.3 6.3 6.3 6.3 6.3 6.3 package ¹Luvitec K17. ²Luvitec VA64.

Two comparable compositions in Table 3 were tested in V-belts, Comp. Ex.1 and Ex. 6, in Comp. Belt A and Ex. Belt B, respectively. The V-beltswere constructed as shown in FIG. 1, with the overcord and undercordboth made of the respective example compound. The belt pitch length was45 inches, overall thickness 0.55 inches, top width 1.25 inches, and Vincluded angle 24°. A different adhesion layer composition was used, butthe same in both belt constructions. The same cord was used in both beltconstructions. The belts were tested on a durability test designed totest CVT belts in a high-load, under-drive situation. The tester wasthus a two-pulley rig with 26° sheaves, with driver sheave having 5-inchpitch diameter and running at 2000 rpm, the driven sheave having7.6-inch pitch diameter and running at 1257 rpm, and a torque load of1003 lb·in. (20 HP). The Durability test results are shown in Table 5.The three control belts tested, Comp. Belt A, exhibited lives of 216,506 and 332 hours, respectively. The three inventive belts tested, Ex.Belt B, exhibited a belt life of 348, 378, and 358 hours, giving acomparable average to the control. Thus, the comparable physicalproperties of these two rubber compositions, indicate comparable beltlife, at least on this test.

TABLE 4 Comp. Comp. Test Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8Hardness (ShA) 90 92 91 92 91 93 94 95 Tensile strength 3594 3360 36643720 3803 3830 3985 3886 (WG) (psi) Elongation % (WG) 11 12 14 10 14 1213 10 M5% (WG) (psi) 2859 2418 2576 2657 2542 2749 2905 2952 M10% (WG)(psi) 2985 3137 3425 3670 3245 3446 3134 2931 Tensile strength 1689 14151789 1701 1820 1755 1883 1879 (XG) (psi) Elongation % (XG) 69 52 64 4364 51 61 63 M5% (XG) (psi) 470 358 385 539 430 476 453 459 M10% (XG)(psi) 795 591 622 842 688 751 712 699 M20% (XG) (psi) 1225 952 1015 12651091 1166 1112 1087 Tear strength- 357 301 334 355 334 344 363 352 (WG)(ppi) Tear strength-(XG) 203 173 178 202 168 189 204 189 (ppi) Tearstrength-aged 350 307 332 381 323 362 361 366 (WG) (ppi)² Tearstrength-aged 189 174 164 202 177 194 188 189 (XG) (kN/m)² RPA G′ (100°C.)¹ 6510 7054 7575 7952 6731 8435 8268 8195 RPA G′ (80° C.)¹ 6402 69227598 7994 6851 8545 8470 8350 RPA G′ (66° C.)¹ 6428 6924 7737 8110 69788632 8653 8577 ¹RPA elastic modulus measured at 6.98% strain, 1.667 Hz(kPa). ²Aged in hot air oven, 70 hrs at 120° C.

The same two compositions were also used to construct some V-belts withstandard BX section V-belt dimensions, i.e., 34° V-angle, 21/32″ topwidth, and 13/32″ overall thickness, labeled Comp. Belt C and Ex. BeltD. These belts were then tested on a V-belt Durability test, a V-beltBackside flex test, and a V-belt Misalignment test. The Durability testincludes 1:1 drive with 4.5″ pitch diameter, 34° sheaves run at 1770 rpmwith 10 HP load. The Backside flex test is similar but run at zero load,3600 rpm, 50-lb total tension, and with a 5″ OD flat backside idler in aspan. The Misalignment test uses the same setup as the Durability test,but the driven sheave is shifted out of alignment by 1°. The results ofthese three tests, also shown in Table 5, indicate comparableperformance between the inventive belt and the control. Again, thesebelt results indicate that natural cellulosic fibers may be a suitablereplacement for some or all of the chopped aramid fibers often found inhigh-performance V-belts.

TABLE 5 Comp. Belt A Ex. Belt B (based on Comp. (based Belt Type Belttest¹ Ex. 1) on Ex. 6) CVT Belt Durability test life (hrs) 216/332/506358/378/348 Comp. Belt C Ex. Belt D V-Belt Durability test life (hrs)564/562 472/457/342 Backside flex life (hrs) 25/44/49 49/28/25Misalignment test life (hrs) 141/73/95 119/73/70 ¹multiple belts weretested and individual lives reported.

In a second series of rubber compound examples, the effect of adding PVPto a CR composition with kenaf, jute, or flax cellulosic fibers wasstudied. The compositions listed in Table 6 were mixed as in the firstseries. The CR measurement results are shown in Table 7. It was foundthat the addition of PVP into the CR compounds having cellulosic fibersincreased the compound elastic modulus (G′), tensile strength, tensilemodulus and tear strength. For the most part, the results do not showthe same level of improvement in properties as for the EPDM compounds.This is believed to be explainable on the basis of the difference inpolarity between EPDM and CR. In particular it is believed that EPDM,being less polar than CR, benefits much more from the addition of apolar polymer such as PVP when it comes to dispersing the cellulosicfibers. Nevertheless there were some notable advantages from the use ofPVP blended with CR with cellulosic fibers.

TABLE 6 Comp. Comp. Comp. Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex.15 Ex. 16 Ex. 17 CR 100 100 100 100 100 100 100 100 100 Kollidon 12 PF —8 — — 8 — — 8 — Kollidon 17 PF — 8 — — 8 — — 8 Kenaf 37.2 37.2 37.2 — —— — — — Jute — — — 37.2 37.2 37.2 — — — Flax — — — — — — 37.2 37.2 37.2Fillers¹ 74 74 74 74 74 74 74 74 74 Other Additives² 18.2 18.2 18.2 18.218.2 18.2 18.2 18.2 18.2 Cure package 8.1 8.1 8.1 8.1 8.1 8.1 8.1 8.18.1 ¹carbon black, silica, etc. ²anti-degradant, plasticizer, ZnO,process aid, etc.

A first advantage to note is that the usual marching modulus of CRdisappears, replaced by a nice cure plateau in the MDR cure results ofTable 7. This is indicated by the much shorter t90 result (time to 90%of full cure). In control compounds study, Comp. Ex. 9, 13 and 16, t90is near the end of the 30 minute test because of the gradual, continualincrease in modulus. But the Examples in Table 7 plateau, giving a muchshorter t90. This effect could be advantageous, depending on theapplication. Depending on the degree of cure desired, the cure systemmay need adjustment to match the cure state of a PVP/CR blend rubber toa CR control rubber.

A second notable result is a significant improvement in elongation forthe flax examples when PVP is added, as in Ex. 16 and 17, relative tothe Comp. Ex. 15 with no PVP. This also seems to correlate with animprovement in modulus and in tear strength (“C-Tear”) for the sameflax-filled compounds.

TABLE 7 Comp. Comp. Comp. Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex.15 Ex. 16 Ex. 17 t90 (min.)¹ 19.5 8.2 8.6 18.0 7.4 8.9 16.0 7.7 8.1 (MH− ML) (lb.-in.)¹ 35.0 30.3 30.5 31.9 25.1 28.0 36.5 26.5 30.7 Tensilestrength (WG) 1636 1500 1430 1631 1270 1318 2291 1261 1309 (psi)Elongation % (WG) 171 142 164 135 143 134 19 62 138 5% Mod. (WG) (psi)717 771 824 834 1013 1099 985 1152 1555 10% Mod. (WG) (psi) 1020 915 945936 1121 1531 1146 1257 2198 20% Mod. (WG) (psi) 1217 969 972 954 10961630 — 1221 1726 Tensile strength (XG) 1185 1012 971 965 745 942 1174870 973 (psi) Elongation % (XG) 149 131 127 92 88 136 79 114 129 5% Mod.(XG) (psi) 247 414 526 376 442 479 410 516 446 10% Mod. (XG) (psi) 370516 628 551 550 567 627 631 561 20% Mod. (XG) (psi) 541 580 670 751 600607 914 678 636 C-Tear (WG) (ppi) 268 238 255 260 240 252 262 264 285C-Tear (XG) (ppi) 171 157 150 147 147 173 161 166 178 aged C-Tear 246259 271 252 279 256 277 285 293 (WG) (ppi) aged C-Tear 132 163 174 142157 167 147 180 184 (XG) (ppi) G′ at 100° C. (kPa)² 4779 6317 6558 64976108 6202 7668 6543 7141 G′ at 80° C. (kPa)² 5161 6671 6975 7010 66776648 8316 7251 7382 G′ at 66° C. (kPa)² 5512 6940 7463 7434 7254 71288879 7913 7512 ¹MDR, 30 min @ 160° C. ²RPA2000, 6.98% strain, 1.667 Hz.

Thus, rubber compositions a according to various embodiments of theinvention may be useful in belts, hose, and other dynamic rubberarticles. These compounds utilize “green” reinforcing fibers, i.e.,derived from natural, renewable resources and biodegradable.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the scope of theinvention as defined by the appended claims. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods, and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps. The invention disclosed herein may suitably bepracticed in the absence of any element that is not specificallydisclosed herein.

What is claimed is:
 1. A rubber composition comprising a base elastomer,polyvinylpyrrolidone, a cellulosic fiber, and a curative.
 2. The rubbercomposition of claim 1 wherein the base elastomer is one or moreselected from the group consisting of ethylene elastomers, nitrileelastomers, and polychloroprene elastomer.
 3. The rubber composition ofclaim 1 wherein the base elastomer is an ethylene-alpha-olefinelastomer.
 4. The rubber composition of claim 1 wherein the baseelastomer is a polychloroprene elastomer.
 5. The rubber composition ofclaim 1 wherein the cellulosic fiber is one or more natural fiberselected from the group consisting of kenaf, jute, hemp, flax, ramie,sisal, wood and cotton.
 6. The rubber composition of claim 1 wherein thecellulosic fiber is one or more selected from the group consisting ofkenaf, jute, hemp, and flax.
 7. The rubber composition of claim 1wherein the cellulosic fiber is one or more bast fiber selected from thegroup consisting of kenaf, jute, hemp, flax, and ramie.
 8. The rubbercomposition of claim 1 wherein the cellulosic fiber is one or more bastfiber selected from the group consisting of kenaf, jute, and flax. 9.The rubber composition of claim 1 wherein the cellulosic fiber is aman-made material.
 10. The rubber composition of claim 1 wherein thepolyvinylpyrrolidone is present in an amount of 5 to 50 parts weight perhundred parts of the base elastomer.
 11. The rubber composition of claim1 wherein the cellulosic fiber is present in an amount of 1 to 50 partsweight per hundred parts of the base elastomer.
 12. A power transmissionbelt comprising a reaction product of the rubber composition of claim 1.13. The rubber composition of claim 1 after having been vulcanized orcured.
 14. A rubber composition comprising: an ethylene-alpha-olefinelastomer; polyvinylpyrrolidone; a cellulosic bast fiber selected fromthe group consisting of flax, jute, and kenaf; and a curative.
 15. Therubber composition of claim 14 wherein the polyvinylpyrrolidone ispresent in an amount of 5 to 50 parts weight per hundred parts of theelastomer.
 16. The rubber composition of claim 15 wherein the cellulosicfiber is present in an amount of 1 to 50 parts weight per hundred partsof the elastomer.
 17. A power transmission belt comprising a reactionproduct of the rubber composition of claim
 16. 18. A dry, vulcanizable,rubber composition comprising a base elastomer, polyvinylpyrrolidone, acellulosic fiber, a filler, and a curative.